1. Field of the Invention
This invention relates to a high-hardness precipitation hardening steel suitable to a material for a metallic mold to be used for forming of plastics (synthetic resin), for example, which is required to surpass in specular gloss.
2. Description of the Prior Art
Heretofore, carbon steels and low-alloy steels have been widely used as a material for a metallic mold used for forming plastics.
In the metallic mold for forming plastics, a pattern is formed on an inner surface of the metallic mold through photoetching to transfer the pattern on moldings.
In this case, it is required for performing photoetching uniformly on the metallic mold in order to transferably form the pattern on the moldings finely and neatly.
However, in the conventional steels such as carbon steels and low-alloy steels, there is a problem in that it is practically difficult to perform uniform photoetching since structure and hardness of the steel become discontinuous among weld metal, heat-affected zone and base metal when the photoetching is performed after padding.
As a die steel which is possible to solve the aforementioned problem, a precipitation hardeness steel of Mn-Ni-Al-Cu-Mo-Fe system is disclosed in Japanese Patent Disclosure (KOKAI) No. 55-28384/80.
In this steel, it is possible to minimize the variation of the hardness among the weld metal, the heat-affected zone and the base metal, therefore possible to perform the photoetching uniformly.
The metallic mold causes a flash or burr of the moldings at a portion between die faces when a depression is formed on the die face of the metallic mold by abrasion or bite of the plastic material between the die faces, and such the problem becomes serious especially in the recent situation where harder plastic materials including filler materials or so become to be used. Accordingly, there is a problem since it is not possible to respond sufficiently to the demand for extending life-time of the metallic mold.